Since the manufacture of the first electrical apparatus, the makers of such equipment have recognized the necessity for protection of the delicate internal circuitry and components of such apparatus from the physical environment of the user. Early election tubes, for example, in the first commercially available radio receivers, were rountinely packaged in a sturdy oak or metal cabinet together with their associated components. As electrical technology advanced, new materials were utilized for the enclosure, but nevertheless, the exposure of the internal electrical components of any electrical apparatus to the environment has always been strictly limited. In many cases, the protection designed was both for the benefit of the electrical apparatus and for the use. The electrical apparatus was subject to breakage by impact from external objects, misuse, and damage resulting from exposure to dust, moisture and other atmospherically-born contaminants. Likewise, the internal electrical components often presented their own set of hazards to the user, among them, electric shock, radiation, high heat levels and unwanted electrical interference, in the form of radio frequency or similar electrical emissions which, if not shielded, could interfere with the operation of other electrical equipment in the same environment.
For these reasons, a variety of methods of protection of electrical circuits have been utilized. Most recently, with the advent of printed circuit boards of various compositions, it has been common to utilize extremely compact enclosures, and to take advantage of the relatively planar configuration of the printed board circuitry to allow mounting of the entire electronics carrier within the enclosure on brackets, stand-offs, screws and the like.
However, a second significant phenomenon, with the advent of large scale integration of circuits, has added a new dimension to the demands for versatile enclosures for the aforestated integrated electronic circuit carriers. Many current microprocessors and microprocessor-based controllers and their associated support circuitry utilize a "bus-oriented" circuit design. Basically, this type of design contemplates that most, if not all, power, signal, clock, data and address lines are open and unterminated in many applications, thereby allowing the interface of each bus-oriented electrical component to a theoretically infinite number of similar bus-oriented electrical components. For example, a typical eight bit microprocessor is equipped with 16 address lines and eight data lines. A serial or parallel interface integrated circuit, by way of further example, may similarly be equipped with an identical, electrically compatible set of address and data buses. In theory, a typical 16 bit address line is capable of addressing over 65,536 individual and discreet addresses. In theory then, over 65,536 individual and compatible components can be addressed by the 16 address lines, simply by electrically connecting any of the potential devices to the same bus to which the microprocessor's data and address lines are connected. This standardized approach to circuit design has resulted in a need for methods of quickly and easily connecting and disconnecting peripheral electronic devices to such data and address buses.
In typical microcomputer applications, such attachments are commonly made through the use of pin or edge card connectors located on the main circuit board. In applications where opening the microcomputer or electrical component's case for insertion and removal of peripheral devices is not practical, it is common to have an exposed electrical connector for the bus, typically in the form of a multiple conductor edge card connector or multi-pin plug and socket arrangement.
While such arrangements are often suitable for relatively fixed, nonportable installations, the interface so designed in current electrical equipment is often not particularly sturdy, and usually disparate in structure and appearance from the principal component, creating problems in physical connection, and requiring separate and independent design of each of the major components and each of its peripheral devices.
A third and significant problem with enclosures for electrical apparatus currently in use, particularly for printed circuit boards and the like, is the necessity for relatively high precision in the design and manufacture of the enclosure. Because electrical circuit boards are routinely manufactured to very close tolerances, the container in which the electrical circuit board is placed, if it is to be conservative of space, requires the same manufacturing tolerances, resulting in higher cost. Likewise, methods of mounting electrical circuit boards within such enclosures must share the same degree of tolerances, for example, mounting holes for the circuit board and the mounting hardware within the case must be precisely manufactured and aligned.
Moreover, the typical metal or plastic electrical enclosure currently manufactured is routinely manufactured to the specifications of the particular application, that is, the electrical enclosure typically embodies a mutually dependent set of variable dimensions. Enclosures are available in premanufactured sizes of, for example, six inches in length by four inches in width by one inch in depth. As the length of a premanufactured enclosure increases, typically, the manufacture of the enclosure likewise increases the width and the depth. The manufacturer of an electronic circuit board component will typically match its circuit board component size to a commercially available container, or, in the alternative, will commission the manufacture of a specific container for the manufactured component.
It can be seen, then, that a need exists for a new electrical enclosure, which eliminates the requirement for precise manufacturing tolerances in size, allows for easy installation of printed circuit board type materials, is easily variable in overall dimension at low cost, is adaptable to the attachment of supplemental or peripheral electrical components through a common bus connector, and at the same time, is sturdy, has a high degree of integrity in an assembled configuration, and is asthetically pleasing.